" AKC SCIENCE CLASSES"
CLASS 10 TH (CBSE AND MP BOARD)
"CHAPTER 02"
"ACIDS, BASES AND SALTS"
"BASIC CONCEPTS WITH INDEX QUESTION AND ANSWERS"
(BASIC CONCEPTS)
(1). ACIDS are sour in taste and change the color of blue litmus to red.
(2). BASES are bitter in taste and change the color of red litmus to blue.
(3). Acids and some base react with active metals to give out hydrogen gas with the formation of salts.
(4). Acids react with sodium carbonate or bicarbonate to give carbon dioxide gas.
(5). Acids neutralize bases or metal oxides to give corresponding salts and water.
(6). All acid generate H+ ions and all base generate OH- ions in the presence of water and this helps acids and bases to conduct electricity.
(7). The amount of H+ ions or OH- ions in a solution can be measured by the pH scale.
(8). The pH of a neutral solution is 7. Value less than 7 represent an acidic solution while more than 7 an alkaline solution.
(9). Values of pH are very important in living organisms and our digestive system.
(10). Mixing strong nitric acid strong sulphuric acid with water is a highly exothermic process.
(11). Water of crystallization is a definite number of water molecules attached to each formula units of a salt in its crystalline form.
(12). Salt of hydrochloric acid and sodium hydroxide is sodium chloride. It is an important raw material for preparing materials used in everyday life and in industries.
(13). Sodium carbonate is obtained by SOLVAY-AMMONIA PROCESS, i.e., by passing CO2 through sodium chloride saturated with ammonia. The reaction takes place in the following steps:-
Heat
CaCO3(s) → CaO(s) + CO2(g)
(ⅰ). NH3(g) + H2O(l) + CO2 → NH4HCO3(aq)
Ammonium
bicarbonate
(ⅱ). NH4HCO3(aq) + NaCl(aq) → NH4Cl(aq) + NaHCO3(s)
Sodium
bicarbonate
Heat
(ⅲ). 2NaHCO3(s) → Na2CO3(s) + H20(l) + CO2(g)
Ammonia (as ammonium chloride) and carbon dioxide are regenerated and so only limestone and sodium chloride are consumed to produce sodium carbonate.
Sodium carbonate mainly used in detergents and softening of hard water.
(14). Sodium hydroxide is an important alkali used for laboratory work. It is produced by electrolysis of sodium chloride (CHLOR-ALKALI PROCESS).
(15). Baking Powder is chemically sodium bicarbonate. It is used as a cooking agent and in fire extinguishers as per the following reaction:-
2NaHCO3 + H2SO4 → Na2SO4 + 2H2O + 2CO2
(Conc.)
A steam of CO2 is produced which cuts off the supply of air and thus fire is extinguished.
(16). Bleaching powder is calcium oxychloride. This is prepared by passing chlorine gas over slaked lime for a long time.
Ca(OH)2(s) + Cl2(g) → CaOCl2(s) + H2O(l)
Calcium
Oxychloride
It is mainly used for bleaching clothes and for disinfecting drinking water.
(17). CaSO4.½ H2O is known as plaster of Paris. When wetted with water it sets to hard porous mass within 10-15 minutes. It is prepared by heating gypsum to 120-130℃.
(18). The interaction of a salt with water to give an acid and a base is called salt hydrolysis.
(19). The solution obtained as a result of hydrolysis may be acidic, basic or neutral depending upon the nature of salt.
(20). Salts of strong acid and strong base like sodium chloride (NaCl), sodium sulphure (Na2SO4) give neutral solution. Salts of week base and strong acid like ammonium chloride (CuSO4) give acidic solution. Salts of weak acid and strong base like sodium carbonate (Na2CO3), potassium acetate (CH3COOK) give basic solution.
NCERT INTEXT QUESTIONS(PAGE 18).
Q:-01:- You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Ans:- Divide the red litmus paper in three parts and dip each part in three test tubes. The test tube in which red litmus paper turns blue contains basic solution. The blue litmus paper so obtained is dipped into the remaining two solutions. The one which turns blue litmus paper red again is an acidic solution. The third tube in which there is no change of color contains water.
NCERT INTEXT QUESTIONS (PAGE 22).
Q:-01:- Why should curd and sour substances not be kept in brass and copper vessels?
Ans:- Curd and sour substances are acidic and acids react with brass and copper and so are not kept in brass and copper vessels.
Q:-02:- Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
OR
Name the gas liberated when an acid reacts with a metal. Illustrate your answer with an example giving the balanced equation for the reaction involved. How would you test the gas evolved?
Ans:- (ⅰ) H2 gas is liberated when an acid is reacts with a metal.
(ⅱ) Illustration:- Take some zinc granules in the test tube. Add about 5 ml dilute hydrochloric acid slowly. Soon the reaction between zinc and hydrochloric acid starts and hydrogen gas is evolved.
Zn + 2HCl → ZnCl2 + H2
(ⅲ) Test for H2 gas:- H2 gas is not soluble in water. When passed through soap solution, it gets trapped into bubbles which burn with explosion.
Q:-03:- Metal compound A react with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Ans:- Since the end product is calcium chloride and the gas formed extinguishes a burning candle, it is CO2, the metal compound A must be calcium carbonate. Hence, the reaction between calcium carbonate and hydrochloric acid is as follows :-
CaCO3 + 2HCl → CaCl2+ CO2 + H2O
NCERT INTEXT QUESTIONS (PAGE 25).
Q:-01:- Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character.
Ans:- H+ ions in aqueous solution are responsible for acidic character. HCl, HNO3 etc., generate H+ ions in water while C2H5OH and glucose do not do so, and hence do not show acidic character.
Q:-02:- Why does an aqueous solution of an acid conduct electricity?
Ans:- Acids give ions in aqueous solution and in solution current is carried through ions. Thus aqueous solution of an acid conducts electricity.
Q:-03:- Why does dry HCl gas not change the color of the dry litmus paper?
Ans:- Dry HCl gas does not generate H+ ions and hence does not change the color of dry litmus paper.
Q:-04:- While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Ans:- When an acid is mixed with water, there is evolution of a large amount of heat. Therefore, acid is slowly added to water. If on the other hand, water is added to acid, it might spill on your body and clothes due to explosion and evolution of sudden and large amount of heat.
Q:-05:- How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Ans:- When a given amount of an acid is added to water, there are a fixed number of hydronium ions per unit volume of the solution. On dilution the number of hydronium ions per unit volume decreases and concentration of hydronium ion decreases.
Q:-06:- How is the concentration of hydroxide ions (OH) affected when excess base is dissolved in a solutions of sodium hydroxide?
Ans:- The concentration of hydroxide ions will increase when excess base is dissolved in a solution of sodium hydroxide because the amount of hydroxide ions per unit volume increases. This happens only when base added dissolves in water. If the base is not soluble in water, the concentration of hydroxide ions remains constant.
NCERT INTEXT QUESTIONS (PAGE 28).
Q:-01:- You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Ans:- Solution A has more hydrogen ion concentration. Solution A is slightly acidic and solution B is slightly basic.
Q:-02:- What effect does the concentration of H+ (aq) ions have on the nature of the solutions?
Ans:- More the concentration of H+ ion, higher the acidic nature of the solution.
Q:-03:- Do basic solutions also have H+ (aq) ions? If yes, then why are these basic?
Ans:- Basic solutions have H+ (aq) ions, But these are far less in number than OH- ions counts for their basic nature.
Q:-04:- Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium hydroxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Ans:- Plants work well in the pH range 6-8. So when the soil becomes acidic, farmers treat the soil fields with bases like quick lime or slaked lime or chalk.
NCERT INTEXT QUESTIONS (PAGE 33).
Q:-01:- What is the common name of the compound CaOCl2?
Ans:- Bleaching powder.
Q:-02:- Name the substance which on treatment with chlorine yields bleaching powder?
Ans:- Lime Water.
Q:-03:- Name the sodium compound which is used for softening hard water?
Ans:- Sodium Carbonate
Q:-04:- What will happen if a solution of sodium hyrogen carbonate is heated? Give the equation of the reaction involved.
Ans:- Sodium hydrogen carbonate on heating gives sodium carbonate and CO2 gas is evolved.
2NaHCO3 → Na2CO3 + CO2 + H20
Q:-05:- Write an equation to show the reaction between plaster of Paris and water?
Ans:- CaSO4.½ H2O + H2O → 2CaSO4.2H2O
Plaster of Paris Gypsum
ACIDS, BASES AND SALTS || BASIC CONCEPTS WITH INDEX QUESTIONS || WITH EXPLANATIONS. CLICK HERE.
